Drug delivery devices are generally known for the administration of a medicinal product, for example insulin or heparin, but also for other medicinal products, in particular for self-administration by a patient. A drug delivery device may be configured as a pen-type injector which may dispense a pre-set dose of a fluid medicinal product. However, the drug delivery device may also deliver a variable dose of the medicinal product.
Before the first use of the drug delivery device, the user may have to dispense a small amount of the product. Thereby, the effect of manufacturing tolerances of the mechanical components of the drug delivery device may be eliminated. The operation of dispensing a small amount of a product before the first use is also referred to as a priming operation of the drug delivery device. Users who are unfamiliar with the drug delivery device may fail to or incorrectly prime their drug delivery device before dispensing the first dose. Another disadvantage of a drug delivery device requiring a priming operation is that a user might accidently inject a priming dose. Moreover, priming operations result in a waste of the medicinal product as the medicinal product expelled during the priming operation cannot be used to treat the patient.